The present invention relates to a noise attenuation apparatus, and in particular to an apparatus for use in a vehicle muffler to attenuate noise generated by vehicle exhaust. More particularly, the present invention relates to a tubular noise attenuation sock or sleeve fitted on a louvered exhaust tube in a vehicle muffler to intercept exhaust discharged through louvers formed in the exhaust tube.
Mufflers typically include a plurality of exhaust tubes for conducting hot exhaust gases emitted from the exhaust manifold along a variety of paths through the muffler. A plurality of separate sound absorption chambers are defined in the muffler by baffles or partitions and these chambers are connected together by the exhaust tubes to guide the flow of exhaust gases passing through the muffler to the vehicle exhaust pipe.
High-frequency noise generated by engine exhaust can cause unacceptable "in-car" and "pass-by" sound quality. Typically, vehicle mufflers are configured to include some type of device for attenuating high-frequency exhaust noise. One aim of the present invention is to attenuate high-frequency exhaust noise in a muffler using an improved filter that is easily installed in any of the sound absorption chambers of a muffler at low cost.
It is known to pack one or more of the sound absorption chambers in a muffler completely with an absorptive fibrous material to attenuate sound in the muffler. For example, U.S. Pat. No. 4,396,090 to Wolfhugel shows a muffler in which each absorption chamber is completely filled with mineral wool. Although sound attenuation of certain higher frequency ranges is achieved using such chamber-filling materials, the manufacturing cost of such a design is high because of the large quantity of fibrous material needed to fill one or more of the muffler sound absorption chambers.
It is also known to cover louvers formed in an exhaust flow tube using a hollow sheet-metal shell or other "cover tube assembly" to provide a high-frequency attenuation chamber mounted on an exterior surface of the exhaust flow tube. For example, U.S. Pat. No. 3,388,768 to Heath et al. shows a plurality of such hollow shells attached to exhaust flow tubes to cover louver banks formed in those tubes and establish a gas-tight attenuation chamber. Other examples are provided in U.S. Pat. Nos. 2,115,113 to MacKenzie et al. and 2,934,161 to Powers.
The manufacturing complexity and cost of producing a muffler assembly capable of attenuating high-frequency noise generated by engine exhaust using conventional cover tube assemblies is relatively high. For example, the individual hollow sheet metal shells must be made and attached to the exhaust flow tubes to provide high-frequency attenuation chambers on the exhaust flow tubes. Furthermore, each conventional cover tube assembly typically provides a single high-frequency attenuation chamber that is small in comparison to the muffler sound absorption chamber in which it resides. Essentially, exhaust discharged into such a conventional gas-tight cover tube assembly is retained therein and not permitted to expand into the surrounding muffler sound absorption chamber where low-and mid-range frequency noise generated by such- exhaust could also be attenuated.
One object of the present invention is to provide a filter for attenuating high-frequency engine exhaust noise that is easily installed in a muffler at low cost.
Another object of the present invention is to provide a filter configured to attenuate high-frequency exhaust noise without unnecessarily hindering maximum attenuation of low and middle frequency noise generated by engine exhaust.
According to the present invention, a noise attenuation apparatus includes an elongated prefabricated fibrous member. The fibrous member is formed to include means for receiving an exhaust tube therein so that the fibrous member jackets the exhaust tube to intercept exhaust discharged through louvers or other side discharge apertures formed in the exhaust tube along its length. The fibrous member provides an exhaust-permeable jacket which effectively covers the exhaust tube louvers to attenuate noise generated by the exhaust.
In preferred embodiments, the fibrous member is a cylindrically shaped tube having an aperture extending along its entire length. The aperture is sized to receive a louvered exhaust tube therein so that the fibrous member fits snugly around the louvered exhaust tube.
Illustratively, the fibrous member is made of stainless steel wool spun about a mandrel to provide an open-ended tube sock or sleeve. The sock is configured so that it can be easily slipped onto a louvered exhaust tube as an athletic tube sock is slipped onto an athlete's leg. Once in place, the sock provides a high-frequency noise attenuation filter covering the exhaust-venting louvers in the exhaust tube.
Provision of a stainless steel wool sock on one or more of the exhaust tubes in a muffler makes the practice of completely packing the interior of a muffler with steel wool no longer necessary. A significant cost savings is thereby achieved because the amount of steel wool used to construct enough socks for a muffler is substantially less than the amount of steel wool that would be needed to fill the interior of a muffler. Such a sock also eliminates any need to mount a cover tube assembly on such exhaust tubes to cover the louver openings in formed in those exhaust tubes, thereby reducing manufacturing complexity and cost. In addition, such a sock is constructed of exhaust-permeable material so that engine exhaust discharged through such louver openings is expanded into the larger volume sound absorption chamber in which the sock resides. This expansion effectively causes low and mid-range frequency noise in the exhaust discharged through the louver openings to be attenuated in the sound absorption chamber at the same time that high-frequency noise in such exhaust is attenuated in the exhaust-permeable sock.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.